Traditional gravity cups for paint sprayers usually have a cup-shaped tank, on whose lower side, an opening with a connecting part for the detachable affixing of the tank on the upper side of the paint sprayer is provided. The connecting part usually consists of a connecting piece inserted into the tank bottom, which has an external thread for screwing into a corresponding thread opening on the upper side of the paint sprayer. As a rule, the cup-shaped tank is closed on its upper side by a suitable cover, which is meant to prevent an undesired discharge of the paint.
Gravity cups, which comprise a cup-shaped tank and a cover with a hollow-cylindrical connecting part that can be placed on it, are already known from WO 01/12337 A1, WO2004/037433 A1, EP 1 366 823 A1, and EP 1902786 A1. The connecting part there comprises a connecting piece shaped directly on the tank cover, for a quick connection of the gravity cup to the paint sprayer. With the gravity cup of EP 1902786 A1, furthermore, a quick-connect thread, in the form of a four-turn pitch thread with external thread turns on the upper external circumference of the tank and corresponding internal thread turns on the inside of the cover is provided for the tight connection of the cover with the cup-shaped tank. The four external thread turns on the tank are uniformly distributed over the external circumference of the tank and arranged in such a way that the beginning of the one thread turn is directly over the end of the next thread turn. In this way, the cover can be firmly screwed with the tank by a more or less fourth rotation.
As a result of a nonhomogeneous rigidity of the tank sealing border around the external circumference of the tank, and wall thickness aggregations formed during the injection molding of the tank distributed nonuniformly
over the circumference, the tanks known from the state of the art tend to have leaks, especially with a local deformation if the tank is compressed when it is being manually handled in the upper rim area.